It is the purpose of this research program to study human and experimental animal skin in vitro and in vivo to determine the role of the nonkeratinizing intraepidermal Langerhans Cell. Recent work indicates that Langerhans cells form an independent cell population. However, there is yet no definite function which can be assigned to this cell. A cytochemical approach combining the techniques of electron microscopy, autoradiography and organ culture will be used. The relation of Langerhans cells to keratinization as well as various disease states, both benign and malignant, will be examined using embryonic skin, adult general body epithelium, and experimentally- altered squamous metaplasia of transitional epithelium.